Debian packaging with pkgr

Hi,

This pull request is a work in progress to make Gitlab easily packageable with [pkgr](http://github.com/crohr/pkgr). Basically I'm trying to make the main configuration available through environment variables, and making the necessary changes so that it can be run through the Rails heroku buildpack without error.

You can see a result of this work at <http://deb.pkgr.io/crohr/gitlabhq/>, where I've managed to automate the making of a debian package based off the master branch.